The present invention relates to a joint prosthesis with a cup-shaped supporting part in which a ceramic insert is secured by a conical clamp.
Joint prostheses are known that have a metallic supporting part and an insert contained therein. The metallic supporting part is anchored in the bone of the patient. The insert forms a wear-resistant sliding surface against which the joint ball of the bone or another joint prosthesis presses. In so-called hard-sliding pairs, at least one part of the joint connection, the insert for example, is made of metal. The fastening of the metal insert in the supporting part which likewise consists of metal is performed with the aid of a polyethylene coupling. The polyethylene coupling is subjected to wear by microrelative movements. This wear is not so serious as frictional wear but the seat of the insert is loosened and abrasion enters the tissue and acetabulum.
U.S. Pat. No. 5,282,864 describes a joint prosthesis in which a metal insert is anchored in a metal supporting part by screws. The insert consists of a cobalt-chromium alloy while the supporting part is made of a titanium alloy. As a result of this design for the joint prosthesis, there is a risk of frictional corrosion and galvanic corrosion. During corrosion, the metals give off toxic ions that can harm the patient.
To overcome these disadvantages, ceramic inserts are used in the metallic supporting parts. Since ceramic materials can be machined only with difficulty, they are usually fastened in the supporting part by conical clamping. An example of this is described in EP 0 649 641 A2.
During conical clamping, considerable tensile stresses develop in certain zones of the insert because the initiation of force cannot be controlled. Although ceramic materials are very hard and resistant to compression, they can accept tensile forces to only a limited degree. This means that thin-walled ceramic inserts in particular cannot be made for technical reasons.